1. Field of the Invention
The present invention relates to a camera, and more particularly to an attachment lens for facilitating close-up photography in front of a camera lens.
2. Description of the Prior Art
Applications of digital cameras currently are very mature and popular so that they almost can have replaced conventional film cameras. As film cameras, digital cameras may be roughly divided into single lens reflex (SLR) cameras and compact cameras, wherein the latter ones are in the majority because of convenience, cheapness and easy operation. However, the compact cameras are equipped with a fixed (uninterchangeable) lens, which usually has a focal length of 35˜105 mm (equivalent to 35 mm film camera) and a minimum focus distance of 50 cm. It can not satisfy the requirement of close-up photography or macrophotography. There may be some high level compact cameras that have so-called close-up photography function of 1 cm to 5 cm. However, they can only provide closer focusing distance instead of providing sufficient optical magnification. Therefore, it's not really capable of close-up photography (the ratio of an image size to an object size is at least 1:4). For the users with a demand on close-up photography, adding an attachment lens, which has a function of magnification, in front of a compact camera's original lens is necessary unless an expensive, heavy, and complicated SLR camera with a close-up lens and a close-up flash is adapted.
Currently, there are various attachment lenses on the market, such as U.S. Pat. Nos. 5,781,807, 5,541,686 and 4,755,833 etc. Those configurations are mainly to install a fixed magnifying lens or glass in front of the original camera lens, and further equipping with a secondary flash (as element 52 in '807) or adding a bent light guide cover (as element 35 in '838) on the original camera flash). However, such current attachment lenses only can provide a unitary and unvarying magnification. Users can't adjust the magnification depending on practical requirements. They at best can change the working distance ( a distance between a camera and a shot object ) to slightly adjust the magnification. However, the magnification only can be reduced below the predetermined maximum magnification by prolonging the working distance. The maximum magnification still can not be exceeded. Moreover, for some applied occasions of industrial and business photography, cameras and shot objects are usually fixed at a specific position to perform photographing largely and continuously. It's very inconvenient to change magnification by adjusting the working distance. Hence, such current attachment lenses should be further improved.